Although consistent associations between ambient PM pollution and cardiovascular disease have been identified, the exact mechanisms, the time course by which PM causes the toxic effects, and effects of different PM species are not adequately understood. This study investigates clinically relevant arrhythmogenic, cardiac autonomic control, repolarization, myocardial ischemia, blood pressure (BP), inflammatory, coagulation, and fibrinolytic mechanisms and time course of PM2.5 effects (both concentration and species). Specifically, is personal short-term exposure to elevated ambient PM2.5 directly related to: (I) the onset of arrhythmic episodes (2) higher frequency of arrhythmias (3) lower heart rate variability (HRV) indices? (4) prolonged repolarization measured by QT index? (5) ST-segment level? Can this association be totally or partially attributed to the change of HRV and QT? (6) elevated ambulatory BP (SBP, DBP, and PP)? What are the time-courses (from minutes to hours) of the effects listed from 1-6 above? (7) Is personal short-term exposure to elevated ambient PM2.s (24-hour cumulative exposure) directly related to elevated markers of inflammation, blood coagulation, and fibrinolytic activity? (8) Are 24-hour cumulative concentrations of the ambient PM2.5 species, mostly emitted/formed from coal-fire power plant and vehicle combustion, associated with the above endpoints (Hypotheses 1-7)? (9) Are the associations between ambient PM2.5 concentration and cardiac endpoints (Hypotheses 1-7) modified by the types of PM2.5 spec/es? (10) Is there a synergistic interaction between PM2.5and long-term cardiac risk in the above relationships? (II) Are persons with older age, diabetes, and hypertension more susceptible to the above PM2.5 effects? We will (1) Recruit 100 patients with only arrhythmias of moderate frequency;(2) Perform a battery of cardiac tests to determine cardiac structural and functional status;(3) Measure concurrently 24-hour Holter ECG, ambulatory BP, and personal PM2.5 exposure, and derive real-time PM2.5 concentration, EGG, and BP data on each participant;(4) Analyze filters to assess major PM2.5 species;(5) Collect pre- and post- monitoring blood samples to assess inflammation and fibrinolytic activities;(6) Assess long-term risks of cardiac events;and (7) use time-series and cross-sectional analyses (both multivariable linear regression, transition models) to test the above research hypotheses. This study requires multidisciplinary collaborations of environmental, cardiovascular, and biostatistics researchers. The results will allow us to better understand the mechanisms and time course by which PM2.5 affects the cardiac system, and identify factors that lead to differential susceptibility to PM, and guide regulatory agencies in designing air pollution control standards.